Hmm, I am not an expert but I heard that most Kllifish live their entire lives in the wild in puddles, so I would assume that is enough space for a couple. As for the filter questions I am not entirely sure, I currently have some baby shrimp living in a large glass bowl with no filter and they seem to be doing okay, but they are much tinier than your fish would be, but I would imagine with enough plants it would work. You just need to make sure you cycle it completely before you add any fish, since you will be relying on the bacteria to break down the ammonia from your fish.